The development of atherosclerosis has been hypothesized to involve the uptake of modified low density lipoprotein (LDL) by macrophages and other cells within the artery wall. Recent studies have led to the identification of specific proteins that are likely to play direct roles in the modification and subsequent metabolism of LDL. These include 15 lipoxygenase, which is capable of promoting oxidative modification of LDL, and the acetyl LDL receptor, which is capable of binding and internalizing oxidized LDL. Both of these proteins are expressed in macrophages within early fatty streak lesions of the artery wall. The emphasis of the studies proposed in this Unit will be to examine the molecular mechanisms that function to regulate the expression of the acetyl LDL receptor and 15 lipoxygenase genes in macrophages. Experiments will be performed to identify hormones and other regulatory molecules that act to increase or decrease the expression of these genes. Activators of protein kinase C have recently been demonstrated to stimulate acetyl LDL receptor expression, and the mechanisms responsible for this effect will be examined in model macrophage cell lines. To further characterize the mechanisms controlling acetyl LDL receptor transcription , genomic sequences encoding the promoter and upstream regulatory elements have been cloned. Functional characterization of cis active elements will be performed by transfection analysis of wild type and mutant genomic sequences linked to suitable reporter genes. Complementary experiments will be performed in transgenic mice to verify the physiologic importance of cis elements defined In vitro. DNA binding assays will be performed using nuclear extracts prepared from cells that express the scavenger receptor to identify putative transcription factors that direct its expression. Several approaches will be used to purify these proteins, determine their functional importance, and clone their corresponding cDNAs. These studies are expected to lead to an improved understanding of the pathogenesis of atherosclerosis and may permit the development of novel strategies for prevention or treatment.